Since the 18 is no longer in production you shouldn't worry much about class legal sails. If the sail you purchase is the same size or smaller most race comitties will overlook it. You stand the risk of being protested if you race successfully, ie win. Tell them at registration and worst case is a .99 penalty. That said Hobies' white sails are probably the best out there, 7oz dacron if memory serves me right. There are some great used sails available at catsailor and thebeachcats websites. I recently started a conversion of my magnum to a Tiger squaretop main sail which will take the penalty if I race it. Also running a Tiger chute, another penalty. If you are going to buy non-hobie get a square top.